1. Field of the Invention
This invention relates to apparatus for receiving information blocks, each of which includes a data block, from a further apparatus in a duplex communications system and in particular to such apparatus which is arranged to determine if a received information block has been corrupted by transmission and when it has, to request the further apparatus to repeat the transmission of the data block of that information block, the data blocks being stored in a receiver buffer.
2. Related Art
When exchanging information over a noisy channel information blocks can be corrupted so it becomes necessary to implement an Automatic Repeat request (ARQ) scheme if the lost data blocks are to be obtained. Of the known conventional ARQ schemes of stop-and-wait, go-back-N and selective repeat (SR), the last is the most efficient in terms of throughput as only those data blocks in corrupted information blocks are retransmitted. It is especially attractive to use such an SR scheme in communications systems with the noisiest channels, for example those using radio links, where many repeats may be needed.
The repeated data blocks when received in a later transmitted information block will generally need to be placed in a particular position relative to the data blocks already received. This is achieved in prior art systems by including as part of each data block a data block number which the apparatus can use to identify the data block and so position it appropriately.